Now the emulated machine is fastest with the slider all the way to the right, whereas before it was the opposite. Would existing/older configs run either much faster or slower than 3.3.0, until the user adjusts the CPU Idle slider?

It works the same, off when fully left, max when fully right. (But there is one tiny bug, if slider is moved to fully left when CPU idle state is active, it gets stuck in idle state)